A number of different medical and surgical tools include elongated shafts. A device for performing a medical or surgical procedure or a diagnostic evaluation is located at the distal end of the shaft, the end furthest from the practitioner using the tool. Providing the tool with shaft makes it possible to position the device that performs the procedure in the patient at a location that is 5 cm or more below the skin. The presence of the shaft makes it possible to perform a procedure on the patient without having to make a large incision so that the location at which the procedure is performed is essentially exposed to the ambient environment. Exemplary surgical tools with this type of shaft include burs, shavers, forceps, staplers, ultrasonic vibrators, RF tissue ablation and/or cauterization electrodes and cameras used to view inside the patient.
When this type of tool is used, the tool is often directed to the site at which the procedure is to be performed through a portal or channel in the patient. This portal may be one that is established as part of the procedure. Alternatively, the portal may be part of a channel that naturally exists in the patient. Nostrils are an example of one set of naturally present portals in a patient
It is a known practice to provide this type of tool with a shaft that, once inserted in the patient is selectively curved. This is because there are many situations in which it is simply not desirable or even possible to perform the procedure by simply positioning the distal end of the shaft at the site at which the procedure is performed. For example, sometimes the shaft is inserted into a portal that curves. This means that after at least partially inserting the shaft in the portal, the practitioner needs to bend the tool shaft so as to further insert the shaft. During a procedure, the practitioner may want to curve the distal end of the shaft to obtain a minimally obstructed view of the application of the working component to the site to which the component is applied.
One species of a tool with a selectively curved shaft is provided with multiple adjacent segments that are bendable relative to each other. At least one cable extends through the shaft to at least the most distally located segment. Some tools are provided with two, three or four cables. The cables are connected to an anchor adjacent the proximal end of the shaft, the end opposite the distal end. The anchor rotates around at least one axis. A number of these tools are further designed so that the position of the anchor is manually set. The practitioner bends the tool by rotating the anchor to cause the selective tensioning and flexing of the cables. This flexing and tensioning of the cables places a longitudinal load on the shaft from the distal end of the shaft. This load is not uniformly imposed on the shaft. There is an arcuate section of the shaft that is subjected to greater loading. The portions of the segments forming this part of the shaft so loaded are compressed or bent towards each other. The bending of these segments is what provides the shaft with its practitioner selected curve.
The above-described tools are able to bend in real time. These tools are sometimes useful for applying a head to tissue so that head is laterally spaced from an extension of the longitudinal axis that extends from the housing or body of the tool.
Nevertheless, there are some tools for which to date, it has been difficult to incorporate a shaft that is bendable in real time. One class of tools that it has proven difficult to use with this type of shaft are tools that include heads that are subjected to significant side loading or radial forces. One species of this class of tool are powered surgical tools. These powered surgical tools includes shaver heads and bur heads. When the head of this type of tool is pressed against tissue, the tissue imposes an appreciable amount of force against the advancement of the head. This force is on a line that, relative to the longitudinal axis of the head, extends radially inwardly towards the center of the head. The force thus appears as the side loading of the head. When the head extends from a rigid shaft, the rigid shaft is able to withstand the opposition this force places on the advancement of the head.
However, when the head is located on the end of known bendable shafts, the slack cables do not hold the longitudinally adjacent arcuate sections of the shaft through which these cables extend against each other. The application of a force against the shaft head causes these individual sections of the shaft to shift position relative to each other. The collective movement of these sections of the shaft causes the shaft to deform from the bend desired by the practitioner.
Further, some tools when activated, apply an added force to the head of the tool shaft. These tools are tools that, to function, are rotated. Examples of such tools include burs and shavers. The rotation of these tools places a tangential force on the tool head. For the reasons set forth above, the bendable shafts of known tools often deform from their desired bends in response to the application of these tangential forces.
Eventually, the flexure of the shaft away from the desired shape may be so great that the shaft no longer has the shape required in order to apply the tool head to the tissue. When this event occurs, the practitioner is required to interrupt the application of the tool and reset the tool so the shaft has the desired curvature. Only after the shaft bend is reset is the practitioner able to resume the procedure. Having to so interrupt the performance of the procedure to repetitively reset the shaft curvature goes against one of the goals of modern surgical practice; a procedure should be performed as quickly as possible. This is a desirable goal because it both minimizes the likelihood the exposed tissue is open to infection and the amount of time the patient is held under anesthesia.
Further, after the tool shaft is bent to perform the procedure it is typically desirable to unbend the tool back to a shape that is straight or nearly straight. This unbending is required in order to remove the tool from the portal through which the tool was inserted in the patient. For many current tools, to unbend the tool it is necessary for the practitioner to do more than just release the tension of the cable subjected to tension. It is also necessary for the practitioner to place a tension on the cables previously allowed to go slack. This is because the tensioning of these cables is what causes the previously bent portions of the shaft to return to a shape that is at or near straight. Requiring the practitioner to apply use his/her fingers to apply the force needed to so straighten the tool further contributes to physical fatiguing of the hand.